A. Field of Invention
The present invention relates to switch control of power to light sources, particularly high power consumption light sources, such that the power level to a light source may be increased or decreased as desired. Improved methods of switch control may be applicable to a variety of components within an electrical system, and may be combined with combinational capacitance to comprise a flexible method of power control to a light source. Power to a light source may be adjusted such that the amount of energy consumed and the quantity of light output may be adjusted, compensation may be made for lumen depreciation and other losses that occur during operational life of the light source, constant or near-constant light output may be maintained, or otherwise.
B. Problems in the Art
Electrical systems operating light sources may benefit from power control for a variety of reasons including, but not limited to, energy conservation and the preservation of the quantity of light output.
High power light sources, such as those used in sports lighting applications, may readily consume considerable amounts of energy per hour; this is due in part to the plurality of light sources typically utilized in a given application. Therefore, improvements over the current state of the art in terms of energy conservation may produce significant benefits. One method of addressing energy conservation is to operate a light source at reduced power levels during off-peak operating conditions (e.g. for a typical sports lighting application, operating at a high power setting during tournament play versus operating at a low power setting during practice). Electrical systems with preset high/low power settings are well known in the art; methods of addressing energy conservation by operating at reduced power levels for said electrical systems may be found in U.S. Pat. No. 4,994,718 and commercially available from Musco Lighting, LLC, Oskaloosa, Iowa, USA under the trade name MULTI-WATT™.
Preservation of the quantity of light output is a concern for many light sources, particularly those which may experience lamp lumen depreciation (LLD), a condition in which the amount of light the source produces diminishes over its operating lifespan. One example of a light source that experiences LLD is a high intensity discharge (HID) lamp (e.g. model MH 1500W/HBU from Venture Lighting International, Solon, Ohio, U.S.A.); this type of lamp is typically used in wide area lighting applications such as sports lighting. FIG. 1 illustrates a generalized light output curve 2 for a light source that experiences LLD. As can be seen from FIG. 1, LLD tends to produce a significant decrease in light output (as evidenced by the hatched area) over the cumulative operating life of the light source. During the initial operation of the light source LLD is most severe, as is evidenced by the significant slope 6 of the curve 2 between T0 (0 hours of cumulative operating time) and T1 (200 hours of cumulative operating time). Beyond T1, LLD still produces a decrease in light, albeit at a diminished rate, as evidenced by the shallower slope 8 between T1 and T4 (3000 hours of cumulative operating time).
One method of addressing the diminishing quantity of light output due to LLD or otherwise is to incrementally increase power to the electrical system via capacitance increases over the course of the operating life of the light source. Assume, for example, a metal halide HID lamp operating at 1500 rated operating wattage (ROW) with typical LLD characteristics such as is demonstrated by curve 2 of FIG. 1. A user may incrementally increase power to the electrical system operating said light source at periodic intervals to maintain a constant or near-constant light output. It is of note that the terms “constant” and “near-constant” are used interchangeably in this text with respect to light output. Methods of increasing light output described herein may be made at any incremental value and at any number of increments; thus, while the methods may approach near-constant light output in terms of measurable quantities (e.g. lumens) over the cumulative operating time of a light source, such incremental changes may be made in such small increments over such a long range of values that to a user light output appears to be constant and, thus, does not depart from aspects of the invention described herein.
FIG. 2 illustrates how such periodic increases to operating wattage (see FIG. 3) result in an increase to relative light output (as evidenced by sawtooth line 10) which may prevent significant light loss (as evidenced by hatched area 112) that would otherwise occur (as evidenced by curve 2). To conserve energy and prevent overdriving said lamp later during its operating life as power increases are added to the electrical system, the initial operating wattage of the lamp may be started at a wattage below ROW. For the aforementioned example of a lamp operating at 1500 ROW, a starting wattage of 1050 watt may be utilized with incremental power increases made until the lamp's maximum operating life is met or the operating wattage of the lamp exceeds a maximum (as defined by the lamp manufacturer or otherwise). FIG. 3 illustrates how incremental increases to operating wattage (as evidenced by line 116) to approach ROW (as evidenced by hatched area 114) may produce constant or near-constant light output as illustrated in FIG. 2 (as evidenced by sawtooth line 10); potential savings from operating at wattages below ROW may generally be indicated by hatched area 114.
Electrical systems operating light sources that experience LLD are well known in the art; methods of addressing LLD, including one method of incremental power increases, may be found in U.S. Pat. No. 7,176,635 and commercially available from Musco Lighting, LLC, Oskaloosa, Iowa, USA under the trade name SMART LAMP®.
In the current state of the art, power adjustments to address energy conservation are generally completed by dimming or switching the circuits in the electrical system to achieve preset high/low levels. One way preservation of the quantity of light output in an electrical system may be completed is by adding capacitance at preset times and in preset quantities to a power regulating component (where power regulating component refers to a component operatively in connection between the main power and the light source which has the ability to change power provided to the light source) within the system. However, as will be discussed, there are limitations to using the aforementioned approaches to adjust power to a light source.
1. Energy Conservation—Dimming Circuits
Using sports lighting applications as an example, one common method to conserve energy is to operate a light source at a lower power level when less illumination is deemed acceptable by owners, participants, or by regulations set forth by lighting organizations; one such organization is the Illuminating Engineering Society of North America (IESNA). IESNA Publication No. RP-6-01 recommends minimum illumination levels based on the type of sport, skill level, and number of spectators; however, many sports lighting systems are used for multiple purposes that may require different levels of illumination (e.g. a soccer field that is used for practice but also for tournaments). Such electrical systems would need to be designed for the highest level of illumination required for tournament play based on the skill level of the players and the number of spectators, but would benefit from a lower illumination level available for practice. Operating at a lower power setting (and therefore a lower illumination level) during off-peak operating conditions results in energy conservation.
Generally, one way a sports lighting system operating a light source may switch from a high power setting to a lower power setting is by changing from a higher capacitance state to a lower capacitance state, commonly referred to as dimming the circuit. However, if a sports lighting system operates a plurality of light sources, dimming the circuits requires a plurality of capacitors for each light source. In addition, extra switching components are required to control the capacitors for each light source. For example, in sports or wide area lighting, due to the available space in a pole cabinet 50, FIG. 4A, or other enclosure housing the capacitors, as well as the cost associated with providing dimming for multiple light sources, most capacitor systems used for dimming are limited to a single high/low power setting.
2. Energy Conservation—Switching Circuits
A method to conserve energy in an electrical system operating a plurality of light sources, particularly a sports lighting system, is to utilize switching groups that operate a subset of the total number of light sources for lower illumination levels, and operate the total number of light sources for higher illumination levels. While this method addresses energy conservation, additional light sources are often required to ensure adequate beam distribution to attain illumination uniformity; again see IESNA Publication No. RP-6-01. Adding additional light sources to an electrical system, including the respective switching mechanisms to control the light sources, may add capital equipment cost, as well as cost from increased energy consumption. Additionally, the light sources in different switching groups may accumulate uneven operating hours if some groups are used more frequently than others; imbalance of operating hours may prevent illumination uniformity due to uneven LLD of the light sources.
3. Preservation of Light Output—Changing Capacitance
One approach to preserving the quantity of light output in an electrical system operating a light source is to make incremental increases to capacitance; see aforementioned U.S. Pat. No. 7,176,635. In one embodiment described in U.S. Pat. No. 7,176,635, an electric timer-motor rotates cams that, in turn, actuate switches, relays, or contactors to sequentially add capacitors to the lighting circuit at times determined by the physical configuration of the electric-timer motor and cams (for reference, see FIGS. 3, 10-13 in U.S. Pat. No. 7,176,635). Each cam is configured to rotate to a position that operates a switch at a preset time when additional capacitance is required to increase power to the light source. Generally, such increases in capacitance are utilized to compensate for LLD and to maintain constant light output. The preset timing is generally modeled after lumen depreciation curves for a given light source.